The present invention relates to a stencil printer of the type including an ink drum and a press drum rotatable with a paper or similar recording medium wrapped therearound while pressing it against the ink drum.
In a stencil printer of the type described, heating elements arranged on a thermal head are selectively energized to perforate, or cut, a thermosensitive stencil made up of a thermoplastic resin film and a porous substrate. The perforated stencil or master is wrapped around an ink drum made up of a porous support and a mesh screen. The mesh screen is implemented as a plurality of metallic mesh layers. While ink is fed from an ink feed member to the inner periphery of the ink drum, a press roller or similar pressing means sequentially presses a paper or similar recording medium against the master. As a result, the ink oozes out through a porous portion included in the ink drum and the perforations of the master, printing a desired image on the paper.
This type of stencil printer should preferably have its press drum and ink drum spaced from each other when the paper is absent therebetween. Specifically, when the paper does not exist between the ink drum and the press drum, e.g., in a power-off state or during master feeding or discharging operation, the press drum must be released from the ink drum. Should the press drum directly contact the ink drum, ink would be transferred from the ink drum to the press drum and would thereby smear the rear of a paper during printing. In light of this, the conventional stencil printer includes moving means for selectively moving the press drum into or out of contact with the ink drum.
Assume that the press drum is rotated counterclockwise at the same peripheral speed as the ink drum. Then, when the press drum is released from the ink drum, it moves at a higher peripheral speed than the ink drum due to the particular configuration and operation of the moving means. Conversely, when the press drum is pressed against the ink drum, it moves at a lower peripheral speed than the ink drum. Such a change in the peripheral speed of the press drum is apt to cause a catch mounted on the press drum to fail to catch the paper at an adequate timing. In practice, a variation in the peripheral speed of the press drum is about 1.5 times as great as the peripheral speed of the ink drum, causing the press drum to fail to catch the paper.
Further, with the configuration and operation of the conventional moving means, it is likely that the positional relation between clamping means mounted on the ink drum and the catch of the press drum is varied. This eventually dislocates an image on the paper. It is therefore necessary to mount a new press roller with the greatest care, resulting in extremely difficult assembly.
Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 9-216448 and 9-1914.